Development - Before humans started to develop the landscape, rain would soak into the ground or be transported via rivers out to sea, as part of the natural water cycle. As people have developed our landscape - built roads, houses, towns / cities, industry, etc over our greenspace and constructed below-ground, piped drainage systems - the opportunity for the natural landscape to absorb, filter and slow down runoff has diminished.
As a result, rainfall runoff, also know as surface water runoff, has increased in both volume and in the speed at which it accumulates. This can lead to problems of both flooding and a reduction in water quality in our environment due to pollutants being flushed off hard surfaces, such as roads and roofs, and the capacity of the sewer network being exceeded, which can lead to pollution of the water environment. Runoff that is retained in the sewer network needs to be pumped and treated before being discharge back into the environment, which can be costly and energy intensive.
Existing / Aged Infrastructure Capacity - the existing drainage network - watercourses, culverts and sewers - has finite capacity. In addition, much of the existing sewerage network is a 'combined' drainage system - meaning that both surface water and foul flows are conveyed in the same conduit - and old. As a result, much of the existing drainage network is are already at capacity and susceptible to flooding during times of high flow.
Urban Creep - this is the loss of permeable surfaces within existing urban areas, caused primarily by house extensions and replacing front gardens with impermeable surfaces for parking. Urban creep creates increased runoff which contributes to flooding and impacts water quality.
Population Change and Housing Demand - Population change, a move towards a greater percentage of the population living in larger towns and cities, and the desire to address the shortage of available housing will increase the amount of impermeable area being created within the MGSDP area.
Loss of Historic Watercourses - throughout the MSGDP area there are many areas that lack direct access to an existing watercourse. Often this is due to the historic development of the urban drainage network, where the watercourse may have been 'lost' to the sewerage network. This brings challenges in terms of discharging surface water flows from existing and new development, and providing a route for managing exceedence flows
Climate Change - Scotland's climate is already changing. Over the last century temperatures have increased, sea levels have risen and rainfall patterns have changed, with increased seasonality and more heavy downpours. These changes are projected to continue and intensify over the coming decades. We can expect future changes in climate to be far greater than anything we have seen in the past. Further discussion on this is available via the Adaptation Scotland website.
SEPA has produced national flood maps for the whole of Scotland. The maps show areas which are at risk of flooding from rivers, the sea and surface water. The maps are available online here - https://www.sepa.org.uk/environment/water/flooding/flood-maps/
Flood Risk Management Strategies have been produced for the whole of Scotland. The Strategies explain what causes flooding in high risk areas as well as the impacts when flooding does occur.
Building bigger sewers, pipes, tanks and pumping stations is neither a practical nor sustainable approach to tackling these challenges.
The following animation provides as useful overview of the problem and sustainable solutions - Ever Wondered Where the Rain Goes?
The Taking Action page of this website provides further information on what we can all do to reduce the risks and impacts of flooding.